Applying a longitudinal tracer methodology to evaluate complex interventions in complex settings

Long-running multi-faceted intervention studies are particularly problematic in large complex organizations where traditional methods prove too resource intensive and can yield inaccurate and incomplete findings. This paper describes the first use of, longitudinal tracer methodology (LTM), a realist approach to evaluation, to examine the links between multiple complex intervention activities (processes) and their outcomes on a construction megaproject. LTM is especially useful when the researcher has little control over intervention delivery but has evidence drawn from multiple sources to evaluate the intervention activities effects over time. This methodology has rarely been deployed in complex organisational settings and not on a construction megaproject. This paper presents a case study of its use over a period of three years, on 24 construction sites forming London’s Thames Tideway Tunnel (Tideway) megaproject. The study examines the ‘transformational’ power of occupational safety and health (OSH) interventions across the multiple organisations and supply chains in the megaproject. The study shows how the method can be adapted in-flight to accommodate shifting lines of inquiry as the intervention activities progress and change. This feature along with its resource efficient operation, make it any attractive option where interventions are likely to have differential effects across multiple sites of enactment.